Chronic subdural hematoma (CSDH) is an encapsulated collection of blood and blood degradation products layered between the dura mater and the arachnoid membrane [13]. CSDH is a common disease, especially in elderly patients in a neurosurgical department [45]. The reported incidence of CSDH varies from 8.8 to 79.4 per 100000 persons per year, with an increasing trend in elderly patients [2,4,5,37]. The incidence of CSDH increases as the population ages [32,37]. Neifert et al. [32] reported that the incidence of CSDH in the United States is expected to increase significantly from 2020 to 2040, with the majority of cases occurring in elderly patients. Rauhala et al. [37] reported the epidemiological findings of a Finnish CSDH cohort and demonstrated that the incidence of CSDH has nearly tripled in the population aged 80 years or older since 1990. The global population is growing older, and the population aged 80 years or over is projected to triple by 2050 [42] therefore, the healthcare burden related to CSDH will increase in neurosurgical practice.

Symptoms in patients with CSDH include headache, cognitive impairment, gait disturbance, or motor weakness. Although spontaneous resolution can occur, surgical treatment is indicated for symptomatic patients with CSDH [8]. Surgical treatments, including burr hole craniostomy, twist drill craniostomy, and craniotomy, for CSDH remain safe and effective treatment modalities for symptomatic patients [15,23,45]. However, CSDH has a relatively high rate of recurrence, ranging from 10% to 20% for patients treated with surgery [3,23]. Various pre- and post-operative management methods, such as patient positioning or corticosteroid, antiplatelet, and anticoagulant use, may also be associated with outcomes of CSDH [23]. However, to date, there is little level I evidence describing optimal perioperative management strategies [23]. Therefore, it is difficult to properly suggest appropriate treatment and follow-up management strategies.

Well-established clinical practice guidelines can contribute to better management strategies for patients with CSDH. The Neurotrauma Clinical Practice Guidelines Committee of the Korean Neurotraumatology Society was organized to prepare treatment guidelines for the management of patients with traumatic brain injuries. Therefore, the present study aimed to present the current clinical, treatment, and outcome characteristics of CSDH patient in the Republic of Korea through the first multicenter study of a generalized CSDH cohort to provide appropriate CSDH treatment guidelines in near future.

A total of 293 patients were enrolled in this study. There were 208 men (71%), and the median age was 75 years (range, 22–95). Of the 293 patients, 83 (28.3%) were aged 80 years or older. The median body mass index was 23.2 (range, 14.8–33.2), corresponding to the upper limit of the normal range [18]. Hemiparesis and headache were commonly observed symptoms and accounted for 133 (39%) of 293 and 94 (32%) of 293 of complaints, respectively. Seventy-eight percent of the patients were either independent or required assistance while walking before surgery. With a median Markwalder grade [27] of 1, the overall neurological state of the cohort was favorable. Head trauma history was confirmed within 2 months of hospitalization in 133 (45%) of 293 of patients; however, it was not clear in 199 (41%). CT alone or with MRI was used in 279 (95%) of 293 of cases when CSDH was diagnosed. The mean radiological follow-up period was 126.2 days (range, 1–807). The baseline characteristics of the 293 patients are summarized in Table 1.

Recurrence was observed in 17 (5.8%) of the 293 patients. Four of the 17 patients underwent reoperation within 2 weeks of the initial surgery due to an increase in residual hematoma, and mean interval from initial surgery to reoperation was 32.1 days (range, 4–104). On the other hand, in patients whose drainage catheter maintenance period was 1, 2, 3, 4, and 5 days, recurrence occurred in six, five, three, two, and one case, respectively. To identify risk factors for CSDH recurrence, the clinical and radiologic characteristics of the non-recurrence group and the recurrence group were compared and analyzed.

CSDH is a common disease found in neurosurgical departments, and its incidence has increased during the last decades [6,36,45]. Particularly, the incidence of CSDH shows an increasing trend in elderly patients [32,37]. Moreover, the global population, including in the Republic of Korea, is growing older [42]. CSDH had a relatively high recurrence rate despite favorable outcomes following surgical treatment. The recurrence rate of CSDH is reported to range from approximately 3% to 30% [15,19,23,36,45]. Therefore, these factors, including incidence, aging population, and recurrence rate, require further attention for CSDH in neurosurgical practice. However, it is difficult to suggest appropriate treatment and follow-up management strategies for CSDH. To date, there is little level I evidence describing optimal perioperative management strategies [23]. Therefore, we, the Clinical Practice Guidelines Committee in Korean Neurotraumatology Society conducted this pilot study to prepare a treatment guideline for CSDH.

In this study, we analyzed the current clinical and radiological characteristics, surgical factors, and outcomes of CSDH in the Republic of Korea through a retrospective multicenter study. The cohort included a majority of elderly male patients. The median age was 75 years, and 71% of the patients were male. Reports show that brain atrophy progresses with age, and the incidence of spontaneous CSDH related to age is significant [24,26]. The high proportion of male patients may be the result of having differences in cranium anatomy, such as size and asymmetry, and activity compared to females [33]. Most of the patients’ preoperative neurological statuses were not severe, with a median Markwalder grade of 1. The common presenting symptoms were hemiparesis (39%) and headache (32%), and the frequency of symptoms was similar to that in the previous reports [8,36,37].

Surgical treatment, especially burr hole craniostomy or trephination, is considered an effective and favorable first-line treatment for symptomatic CSDH. In this study, all patients underwent burr hole trephination and drainage. The effectiveness and safety of burr hole craniostomy for CSDH have been described in many papers [6,14,15,21,43]. Moreover, Ducruet et al. [12] reported that although burr hole craniostomy was associated with relatively higher complication rates, 9.3% in burr hole craniostomy vs. 2.5% in twist drill and 4% in craniotomy, it had significantly lower recurrence rates compared with the other two procedures. On the other hand, in a systemic review and meta-analysis of 34829 patients with CSDH, Almenawer et al. [3] demonstrated that there was no significant difference in mortality, morbidity, cure, and recurrence rates between twist drill and burr hole craniostomy, but craniotomy as a first-line procedure resulted in significantly higher complication rates.

Although this study was conducted with a relatively small number of seven institutions, the preferred surgical method, such as the location of the burr hole, number of burr holes, use of irrigation, and postoperative management including drainage method and patient’s posture was different for each institution or attending physician. In order to develop appropriate clinical guidelines, it is essential to conduct studies on data and consensus from various regions and multi-institutions rather than single-institutional cohort studies, which are susceptible to bias and methodological pitfalls [11]. Therefore, this study was designed as a pilot study to begin the development of Korean guidelines for the management of CSDH.

Some interesting differences in surgical management such as anesthesia method, number of burr holes, and saline irrigation were noted. Among these 293 patients most underwent single burr hole craniostomy. However, 70% of 293 patients underwent surgery under general anesthesia. Sixty-four percent of patients were postoperatively managed with a flat head position, and 71% were managed using the free drainage method. In terms of postoperative head position, Miele et al. [30] and Abouzari et al. [1] reported opposite conclusions about the effect of postoperative head position on the recurrence of CSDH. However, this remains controversial. If this pilot study could be further conducted and analyzed, it would be helpful in establishing treatment guidelines.

As mentioned above, the recurrence rate of CSDH varies. Previous studies have reported that various factors are associated with the recurrence of CSDH. Hematoma density [19,46], postoperative intracranial air [20], and shorter duration of subdural drainage [46] have been reported as independent risk factors. Moreover, there have been many reports that use of antithrombotic agents increases the incidence and recurrence rates of CSDH [10,35,39]. In our study, several prognostic factors that influenced the recurrence of CSDH were identified in the multivariate analysis : general anesthesia and a separated type of hematoma. Surgery was performed under general anesthesia in 70% of the patients. General anesthesia was negatively correlated with CSDH recurrence (odds ratio, 0.277; p=0.0017). Although it is difficult to compare recurrence rates between general anesthesia and local anesthesia groups, previous studies reported that the recurrence rate was 6–15% in CSDH cases treated with local anesthesia [25,28] and 10–20% in CSDH cases treated with general anesthesia [15,22,40]. More recently, Blaauw et al. [7] reported that there is no significant differences in three-month recurrences (12% vs. 10%, p=0.510) between local and general anesthesia. The characteristics of each cohort and the standard anesthesia method of the neurosurgical facilities might be related to the differences in recurrence rate of CSDH. On the other hand, Surve et al. [41] reported that burr hole surgery for CSDH with local anesthesia has significant advantages in terms of operative time, hemodynamic fluctuations, postoperative complications, and length of hospital stay. Therefore, additional research on the difference in the recurrence rate according to the anesthesia method is necessary, and we suggest a reasonable selection of anesthesia according to age, underlying disease, and cooperative ability of patients and others.

In the separated type of CSDH, fibrinolysis occurs in hematoma, and it is known to be related to CSDH recurrence [31,38]. Jack et al. [16] described that the septations in CSDH are associated with larger postoperative residual hematoma collections requiring repeat surgery. More recently, Miah et al. [29] reported a recurrence rate of 14.4% in a systematic review of 22 studies on CSDH. They also reported that there are several radiological prognostic factors of CSDH recurrence, such as hyperdense components, laminar and separated types of hematoma, and bilateral CSDH [29].

Heavy drinking was a significant risk factor for recurrence of CSDH in the univariate analysis but not in the multivariate analysis. It is difficult to find published studies demonstrating a significant association between alcoholism and CSDH recurrence. Kostić et al. [24] reported risk factors for spontaneous CSDH in elderly patients and showed that the percentage of heavy drinkers in the CSDH group was significantly higher than that in the control group. Chen et al. [9] reported that patients with liver cirrhosis and CSDH are significantly more likely to have serious comorbidities, including mortality rate. However, there was no difference in recurrence rate between the liver cirrhosis and control groups [9]. In this study, there was no significant correlation between recurrence of CSDH and liver function laboratory test results. However, due to the small number of patients with liver disease (n=9), statistical significance could not be confirmed. Drain insertion is an important procedure in burr hole trephination. Although we are unable to comment upon the tip position of the drainage catheter, several studies demonstrated that the position of the drainage catheter had no relationship with recurrence rates [34,44]. On the other hand, 71% of the patients with CSDH were male in this study. Oh et al. [33] reported that the size and asymmetry of the cranium were associated with the occurrence of CSDH, and the differences in cranial anatomy may be related to the findings of this study. However, the association between cranium anatomy and recurrence of CSDH is not well understood. To identify the relationship between cranium anatomy and recurrence of CSDH, further studies on this needs to be conducted.

The limitations of this study include those inherent in retrospective analyses and the relatively small number of cases. In our cohort, the quality of medical records varied among the cases at each institute. The retrospective nature of this study might have created a bias. Moreover, this study was conducted as a pilot study to prepare treatment guidelines for CSDH. Seven out of 45 advanced general hospitals in the Republic of Korea were enrolled to analyze the status of clinical management of CSDH for 1 year. Therefore, further study through the participation of more institutions and expansion of the number of patients is mandatory. Moreover, additional studies are also needed to find other detailed risk factors, such as cranial anatomical differences related to CSDH recurrence. In terms of long-term outcomes, several studies have reported that poor emotional or psychological prognosis and cognitive impairment occur approximately 5 years after CSDH treatment [31,38]. Further studies are needed to suggest the long-term management of CSDH. However, despite these limitations, our cohort study is the first multicenter study to analyze patients with CSDH in the Republic of Korea and contributes to the understanding of the current status of CSDH management in the country.

This retrospective, the multicenter study reported on the current management and surgical outcomes of patients with CSDH and identified several prognostic factors related to CSDH recurrence. The population characteristics of CSDH are similar to those previously reported. Although there were some differences in the surgical technique and management plan at each institution, the effectiveness of surgical treatment for CSDH was confirmed. Therefore, treatment guidelines based on the various characteristics of cases are necessary. Even though this study has limitations as it was a pilot study, we hope that it will contribute to establishing treatment guidelines for CSDH by providing a scientific basis for further studies.